never done a Ka, but the new bumper will show you where the brackets are. Normally bumpers have 2 brackets connected to the bodywork at the back, sometimes the bolts come off from inside the boot once you remove the trim, and sometimes from underneath the car. Mostly the sides just slide onto brackets. Look at the new bumper to judge where they dhouls be. Normally a couple of bolts for each bracket. Or buy a Haynes manual, well worth it if you might tackle anything else yourself...